Electromagnetic (EM) signals in the terahertz (THz) range are being explored for use in imaging applications. For example, EM signals in the THz range may be used to image materials that are opaque at optical frequencies and that provide very low contrast to x-rays. Some applications of THz imaging may include security screening and manufacturing quality control.
EM signals in the THz range used for imaging can be detected using direct or heterodyne-based detection techniques. Direct detection techniques provide limited sensitivity or require cryogenic cooling of the detector electronics. Known heterodyne-based detection techniques provide high sensitivity detection at room temperature using electronic circuits by mixing two EM signals of different frequency from two different signal sources to produce a heterodyne beat signal. The mixing of the two EM signals from the two different sources requires precise alignment of optical elements to ensure that the two EM signals are incident on the same spot on the receiving mixer. The area on which the two EM signals must coincide on the receiving mixer is extremely small and therefore the alignment process can require specialized alignment equipment and can be quite time consuming.
In view of this, what is needed is a technique for detecting EM signals in the THz range that can be performed using electronic circuits at room temperature with reduced alignment requirements.